Document 3e6Dpq8oZeZar8wrMxLqzLo5n

AR226-2322 ^ Charles J Zarzecki 04/03/2003 09:31 AM To: Catherine A Barton/AE/DuPont co: Subject: Re: Beychok A rticle Q C a th ie , First, by "Monday's m eeting", I assume you mean A pril 14? Regarding CW, base on my schedule and yours, I would say a m inim um o f 2 weeks. However, I was at the CW wastewater partitioning team meeting yesterday, and it looks like they w ill only have a sampling plan proposed by Monday. Then they w ill have to im plem ent it, get the results, and then we can m ove ahead w ith the TOXCHEM m odeling. A fter that, we w ill have an em ission rate fo r the wastewater. Looks like it w ill be aw hile before we can do any am bient air dispersion modeling to get definitive results, anyway. As a firs t cut, I guess we can run the stack numbers to see what they look like. Charlie Z. Catherine A Barton ^ Catherine A Barton ' 04/02/2003 04:57 PM To: Charles J Zarzecki/AE/DuPont@ DuPont cc: Subject: Re: Beychok Article Cl C h a rlie , Firs}, thanks fo r taking the tim e to go over Beychok's article thoroughly. I have the same instinctive feeling that you do: to lam bast (yes, its' a great word) the model is a losing battle. W e have to develop a more positive strategy tha t the agency can live w ith. I like your alternative strategy o f fine-tuning our inputs. I want to contact the site guys who did the estim ates to see how much better they think they can get (I'll do that tom orrow). For M onday's m eeting, I want to put together a graphic that shows them som e options. Let me soak on it overnight and run something by you manana. Incidentally, I met w ith the Cworks strategy team and they are happy w ith our modeling plan. Ann Masse wants me to get the em issions inform ation from the site guys by 4/11 so we can start cranking numbers. Help me with this: w hen do y o u th in k we can re a llis tic a ily have th e fir s t rou nd o f a m b ien t a ir num bers? I have to convert my flow diagram into text fo r Ann, and she wants me to put in real dates for deliverables (pending her boys get us the em issions data by 4/11). I'll be in the office tom orrow, but I think you're at hom e. No m atter...w e'll connect. thanks again, E X D 747739 c Charles J Zarzecki i ^ Charles J Zarzecki 04/02/2003 03:14 PM To: Catherine A Barton/AE/DuPont cc: Subject: Beychok Article C a th ie , . I fina lly was able to review the Beychok article on error propagation in dispersion m odeling. This could add fuel to Dave Rurak's fire. It's common knowledge that Gaussian m odels overpredict by a factor o f 2, however, due to error propagation, he says as high as 80X. Also, as fa r as 1-hour concentrations are concerned, the actual averaging tim e for Pasquill's dispersion coefficients range from 3 m inutes to 30 m inutes, depending who you ta lk to. I always thought they were 15-m inute averages. This short-term to 1-hour assumption can be shown (by Beychok) to result in a 2.5X overprediction. However, in my opinion, since the 1-hour period is the basic tim e-step in the ISC (and other) model, an annual average concentration at any given receptor is 8 ,7 6 0 1-hour concentrations divided by 8,760 hours. If it predicts poorly fo r each 1-hour period, then it predicts poorly fo r the whole year. Dave has to understand that the model is a screening tool. The m ore accurate inform ation you put into a model, the greater Ihe accuracy o f the prediction. Instead o f lam basting (is that a real word?) the m odel's 1-hour prediction, we should investigate how to fine-tune the input data and m odel options (e.g, particle settling, hours o f operation, hourly em ission rates, m ore accurate model (AERMOD), etc...). O r, go out and do some sam pling to get the "real thing". W hat do you think? Beychok references about a half-dozen other publications that discuss the shortcom ings o f Gaussian models. Some of them go way back. As you can see, nobody really took them seriously. W hat I am getting at: the regulatory agencies (OEPA, W VDEQ) are not going to want to hear about how bad ISC is fo r particular tim e periods. They may be open to other "accepted" models and to sharpening our pencils. Regards, Charlie Z. EID747740